For many years, variable air volume (VAV) terminal units have been used as components of heating, ventilating and air conditioning systems. An example of such a system is shown in U.S. Pat. No. 5,180,102 (Gilbert et al.).
Such units terminate a run of air duct (in the ceiling of an individual office, for example) and include controls which are activated by, typically, a wall thermostat. Thus, the office occupant can regulate temperature independent of other offices. For just as many years, the main box-like compartments of these VAV terminal units have been internally-lined with insulation. Sometimes, such insulation is covered by a plastic material, metal foil or nylon web. Such internal insulation (which can "sluff" particulates and, with certain coverings, delaminate) is perceived by many to deaden sound. And there is no doubt that it impedes heat transfer through the compartment wall and helps prevent moisture condensation on the unit. U.S. Pat. Nos. 3,283,694 (Dean, Jr.) and 5,147,243 (Inglis et al.) show exemplary apparatus used in air conditioning applications and having such internal insulation.
There are a number of compelling reasons why internal insulation is used. They include ease of manufacture in that it is a straightforward task to apply insulation. Before the cut compartment sheet metal is bent and secured in its final box-like shape (i.e., while it is still "two dimensional" or flat), a single strip of insulation is adhered to that surface which will become the interior surface when the compartment is finally formed. Then the sheet metal is bent and secured to form the compartment as sold.
Another reason relates to control mounting. The smooth, rigid, unobstructed exterior of the compartment presents a very suitable surface on which to mount controls such as pneumatic or electric damper actuators. And such surface, being quite durable, resists abrasion resulting from movement of damper control linkages and the like.
Yet another reason why internal insulation is used relates to the way in which VAV units are installed. Typically, they are suspended from and below a beam-supported permanent ceiling and above and closely adjacent to a lower, "dropped" ceiling of acoustic tile, for example. Unit suspension is by downward-extending hangars attached to the non-covered exterior surface of the unit compartment with screws or the like. Therefore, mounting is quite easy.
And internal insulation is used for another, very pragmatic reason. The outer compartment walls protect such insulation from damage during shipping and mounting.
And quite aside from these reasons, there is a general belief that an insulation-covered compartment interior surface reduces discharge and radiated sound levels. Clearly, users of VAV units are sensitive to increased noise levels and wish to avoid them.
The invention embodies concepts which run contrary to traditional "teachings" of prior art VAV units and which are surprisingly effective in distributing air and helping assure that such air has minimal particulate content.